1. Field of the Invention
The present invention relates to a device for testing light-emitters, particularly the light emitters of pulse oximetry probes.
2. State of the Art
Pulse oximetry is a non-invasive technique for measuring the oxygen content of a subject's blood and is in common usage throughout the world. A pulse oximeter consists of a probe connected by a length of cable to a monitor which includes a display, from which the oxygen content of the subject's blood can be read. Typically, the probe includes two light emitting diodes (LED's) of different wavelengths, and a photodiode: the probe is usually applied to the subject's finger, arranged for the light from the respective LED's to be transmitted through the finger tissues to the photodiode. A ratio derived from photodiode output signals, when receiving light from the different LED's, is used to provide a measure of the blood oxygen content: more specifically, the ratio of the pulsatile component to the non-pulsatile component of the photodiode output when receiving the red light is determined, and a similar ratio is determined for the corresponding components of the photodiode output when receiving the infra red light; then the final ratio is formed between these respective ratios.
Most commonly, pulse oximeter probes are reusable and are accordingly used until they fail mechanically, at which time it becomes self-evident that they are unsuitable for further use. In the meantime, however, the accuracy of the probe is rarely (if ever) checked, because the only means known for doing so are complex and therefore relatively expensive.
We have now found that the components of pulse oximeter probes commonly deteriorate with age: this can lead to a decrease in accuracy. We have also found that "remanufactured" probes are often in use in hospitals, some of which have had replacement components of the wrong specification fitted to them, with the result that these probes are inaccurate.